Imaging the Earth

Make Your Own Globe

Flat maps may be easier to carry around, but there is still a need to make globes so that Earth's geography can be viewed without any directional or spatial distortions. Printing the location of continents and oceans directly onto a round surface would be difficult. Instead, this map of the Earth is printed in flat, roughly triangular sections and then attached to a ball. These sections are called gores.

Make a globe

Using a tape measure, determine the circumference of the ball, making sure that the tape measure circles the ball without wandering away from the "equator."

On a large piece of paper draw a rectangle the same length as the circumference of the ball. The height of the rectangle should be half the circumference of the ball. Draw an equator line through the center of the rectangle, lengthwise.

Cut out the rectangle.

Place the rectangle in front of you horizontally. Fold it in half three times. Unfold the rectangle and there are eight equal sections. Draw a line along each fold. Measure the bottom edge of one section to find its midpoint, and mark that point "A." Mark the end of the equator in that end section "B."

Find the midpoint between A and B as follows: Place the compass point on A. Set the compass radius to a length just short of B and draw a semicircle. Maintaining the same radius, place the compass point on B and draw a second semicircle. The two semicircles should intersect at two points. Draw a straight line through the points where the semicircles intersect, extending the line to a point at which it intersects the equator line. Mark this point "C."
The length of the line from A to C is the radius of the gores.

Attach extra paper to both ends of the original piece (These extensions should be at least the length of the gore radius) Extend the equator line out onto the extra paper at least the distance of the gore radius. This will allow you to move your compass point out along the equator far enough to draw all of the gores.

Set the compass to the gore radius (the distance between A and C). Place the compass pencil on A and the compass point on C. Draw an arc from A to the top of the rectangle.

Maintaining the same compass radius, move the compass pencil to the midpoint of the bottom edge of the next section and place the compass point on the equator. Draw another arc in the same manner. Continue moving the compass and drawing arcs for each of the eight sections.

Turn the paper upside down and repeat the above procedure to draw the opposing arcs and form the gores.

Remove the extra paper from the rectangle.

Create grid lines for transposing the map onto the rectangle as follows: Fold the rectangle as you did in Step 4. Fold once more in the same direction. Unfold the rectangle, and place it in front of you horizontally. Fold it in half, top to bottom, three times. Unfold the rectangle. The rectangle should be divided into 16 sections left to right and 8 sections top to bottom. Cut out the spaces between the gores. Transpose the map from the given to your gores using the gridlines on the diagram and the gridlines (folds) on the gores as a reference.

Tape the strip of gores at one end of the equator to the ball. Wrap the strip around the ball and tape the loose ends in place, taking care to align the equator line.

Glue each gore down against the ball so the tips meet to form the north and south poles.

Make an Orange Globe

To demonstrate the difficulty in making a flat map of a round surface make a map out of an orange peel. Try to peel an orange with an Exacto knife so that you take off the skin in one piece. Make a flat projection of the surface of the orange by laying the peel flat. Does your peel look like the gores from the previous activity?